Method for communication between circuits

ABSTRACT

A first element and a second element of a same device communicate with each other. The first element sends the second element a first piece of information representative of energy supplied by an electromagnetic field supplying power the device. The second element adapts its operating frequency as a function of the first piece of information.

PRIORITY CLAIM

This application claims the priority benefit of French Patentapplication number 1911040, filed on Oct. 4, 2019, the content of whichis hereby incorporated by reference in its entirety to the maximumextent allowable by law.

TECHNICAL FIELD

The present disclosure relates generally to electronic circuits and,more specifically, to the systems in which two circuits are capable ofcommunicating with one another.

BACKGROUND

Many applications are known in which an electronic device is devoid ofan internal power source, such that circuits embedded on this device canonly be activated when sufficient energy is supplied to them,externally, by another device. This is, in particular, the case ofcertain contactless cards which draw, generally from an electromagneticfield emitted by a reader located within range, the electrical energynecessary for the power supply of their circuits. These circuits have,if applicable, a limited electrical power that should be used as well aspossible to guarantee an optimal operation of the device to which theybelong.

Two circuits of such a device can sometimes, as long as they aresuitably powered and after having been activated, communicate with oneanother. An effort is then made to ensure that the communication linkhas the smallest possible number of conductors, in order to take uplimited space in or on the device.

There is a need to optimize the power consumed by two circuits capableof communicating with one another.

SUMMARY

According to one aspect, it is provided to limit the number ofconductors of a link used for communication between two circuits.

According to another aspect, it is provided to transmit informationrelative to outside constraints to the circuits.

An embodiment addresses all or some of the drawbacks of knowncommunication methods.

An embodiment provides a method for communication between a firstelement and a second element, in which: a first channel conveys asynchronization signal; second and third channels convey two datasignals; and fourth and fifth channels convey two signals configured tocontrol an output of a standby mode respectively of the first elementand the second element, the first through fifth channels, beingtransmitted over three or four conductors.

According to an embodiment, the signals conveyed by the fourth and fifthchannels are further configured to control a placement in standby moderespectively of the first element and the second element.

According to an embodiment, the conductors couple, preferably connect,respectively, input-output terminals of the first element toinput-output terminals of the second element.

According to an embodiment, the first element electrically supplies thesecond element.

According to an embodiment, two additional conductors couple, preferablyconnect, the first element to the second element and are respectivelybrought, by the first element, to an electrical supply potential and toan electrical reference potential.

According to an embodiment, the first element is placed in standby modeafter having transmitted a control to the second element.

According to an embodiment, the second element is placed in standby modeafter having transmitted a response to the first element.

According to an embodiment, the first element and the second elementbelong to a same device.

According to an embodiment, the first element controls the placement ofthe second element in standby mode in order to communicate with theoutside of the device.

According to an embodiment, the device communicates with the outside bya radiofrequency signal.

According to an embodiment, the first element is a secure electroniccircuit.

According to an embodiment, the second element is a microcontroller.

According to an embodiment, the second element is coupled, preferablyconnected, to a fingerprint sensor.

According to an embodiment, the fingerprint sensor is part of thedevice.

According to an embodiment, the first element electrically supplies thefingerprint sensor.

An embodiment provides a method for communication between a firstelement and at least one second element of a same device, in which: thefirst element sends the second element a first piece of informationrepresentative of energy supplied by an electromagnetic field supplyingthe device; and the second element adapts its operating frequency as afunction of the first piece of information.

According to an embodiment, the first piece of information is anintensity of an electrical supply current of the device from theelectromagnetic field.

According to an embodiment, the first piece of information is evaluatedby the first element.

According to an embodiment: the first element sends the second element asecond piece of information representative of a remaining time budget ofthe device; and the second element performs a number of operations as afunction of the second piece of information.

According to an embodiment, the second piece of information is evaluatedby the first element.

According to an embodiment: the first element sends the second element athird piece of information representative of a voltage budget of thedevice; and the second element adapts an internal configuration as afunction of this third piece of information.

According to an embodiment, the third piece of information is evaluatedby the first element.

According to an embodiment, the first element supplies the secondelement.

According to an embodiment, the first element is a secure electroniccircuit.

According to an embodiment, the second element is a microcontroller.

According to an embodiment, the second element is coupled, preferablyconnected, to a fingerprint sensor.

According to an embodiment, the fingerprint sensor is part of thedevice.

According to an embodiment, the first element supplies the fingerprintsensor.

According to an embodiment, the device communicates with the outsidewithout contact, by a radiofrequency signal, or with contact.

An embodiment provides a device configured to carry out the method asdescribed.

An embodiment provides a payment card configured to carry out the methodas described.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will bedescribed in detail in the following description of specific embodimentsgiven by way of illustration and not limitation with reference to theaccompanying drawings, in which:

FIG. 1 shows, schematically and in block diagram form, an embodiment ofa near field communication system;

FIG. 2 shows, schematically and in block diagram form, an embodiment ofcircuits of a device of the system communicating with one another by awired link;

FIG. 3 is a sequence diagram of phases of an embodiment of acommunication method;

FIGS. 4A and 4B show timing diagrams of phases of the embodiment of thecommunication method;

FIGS. 5A and 5B show timing diagrams of other phases of the embodimentof the communication method;

FIG. 6 is a timing diagram of still another phase of the embodiment ofthe communication method;

FIG. 7 is a timing diagram of still another phase of the embodiment ofthe communication method; and

FIGS. 8A and 8B show flowcharts of other steps of the embodiment of thecommunication method.

DETAILED DESCRIPTION

Like features have been designated by like references in the variousFigures. In particular, the structural and/or functional features thatare common among the various embodiments may have the same referencesand may dispose identical structural, dimensional and materialproperties.

For the sake of clarity, only the operations and elements that areuseful for an understanding of the embodiments described herein havebeen illustrated and described in detail. In particular, the generationof the exchanged signals and data as well as their interpretation havenot been described in detail, the described embodiments and modes ofimplementation being compatible with the standard techniques forgenerating and interpreting these signals and data.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when referenceis made to absolute positional qualifiers, such as the terms “front”,“back”, “top”, “bottom”, “left”, “right”, etc., or to relativepositional qualifiers, such as the terms “above”, “below”, “higher”,“lower”, etc., or to qualifiers of orientation, such as “horizontal”,“vertical”, etc., reference is made to the orientation shown in thefigures.

Unless specified otherwise, the expressions “around”, “approximately”,“substantially” and “in the order of” signify within 10%, and preferablywithin 5%.

In the following disclosure, a “binary signal” refers to a signal thatalternates between a first constant state, for example a low state,denoted “0”, and a second constant state level, for example a highstate, denoted “1”. The 0 and 1 states of different binary signals of asame electronic circuit can be different high and low levels. Inpractice, the binary signals can correspond to voltages or currents thatmay not be perfectly constant in the high or low state.

FIG. 1 shows, schematically and in block diagram form, an embodiment ofa near field communication (NFC) system.

In FIG. 1, a first near field communication device 1 (READER)communicates with a second near field communication device 2 (CARD).According to this embodiment, the first near field communication device1 is, for example, a contactless payment reader or terminal 1 or amobile telephone having this function. The second near fieldcommunication device 2 is, for example, a contactless payment bank card2.

The terminal 1 includes an antenna 10 (ANTENNA). This antenna 10 is, inparticular, configured to emit an electromagnetic field (EMF) generatedby one or several electronic circuits of the terminal 1, theseelectronic circuits being symbolized, in FIG. 1, by a single functionalblock 12 (FCT). In a case where the bank card 2 is located within rangeof the terminal 1, the electromagnetic field emitted by this terminal 1can then be detected by an antenna 20 (ANTENNA) of this card 2. Theterminal 1 is then said to be operating in “reader” mode, while the card2 is operating in “card” mode.

The card 2 includes, aside from the antenna 20, a first element 21 (SE)or circuit 21 and a second element 22 (BioMCU) or circuit 22. The firstelement 21 is preferably a secure electronic component. According tothis embodiment, in which the card 2 is a contactless payment bank card,the first element 21 can be a microcontroller 21 configured to performsecure tasks, for example operations associated with bankingtransactions between the card 2 and the terminal 1. The second element22 is suitable for processing biometric data acquired by one or severalsensors 23 (SENSOR). The second element 22 is preferably amicrocontroller unit (MCU). The second element 22 can be a genericmicrocontroller unit or a biometric microcontroller unit, in other wordsan electronic component dedicated to the processing of biometric data.

According to a preferred embodiment, the microcontroller unit 22 differsfrom the microcontroller unit 21 primarily in that this microcontrollerunit 22: executes, for an electrical power consumption substantiallyequal to that of the microcontroller 21, more than a millioninstructions per second (MIPS), in particular instructions related toimage processing operations; is capable of managing one or several modesin which its electrical power consumption is greatly reduced, preferablyby several orders of magnitude relative to a nominal operating mode, forexample a low consumption mode at about 50 μA and a nominal mode at 10mA; embeds a greater quantity of RAM than that of the microcontrollerunit 21 (for example 100 kB for the microcontroller unit 22 versus 16 kBfor the microcontroller unit 21) in order to execute biometricalgorithms; and integrates several interfaces, in particular allowingthis microcontroller unit 22 to communicate with the firstmicrocontroller unit 21 and with the sensor 23.

FIG. 1 shows a single sensor 23 (SENSOR) associated with the secondelement 22. This sensor 23 is, for example, a fingerprint sensoraccessible from the front face of the bank card 2. The second element 22is then, for example, a microcontroller steering the acquisition, by thesensor 23, of images corresponding to fingerprints of a user of the card2 and which executes one or several applications for analysis of theseimages. The second element 22 and the fingerprint sensor 23 jointly forma biometric framework (BIOMETRIC FRAMEWORK).

According to this embodiment, the first element 21, in particular,includes: a first transceiver, for example of the universal asynchronoustype, for radiofrequency signals 210 (Radio-Frequency UniversalAsynchronous Receiver Transmitter—RFUART); an energy harvesting module211 (ENERGY HARVESTING); input-output terminals or studs (GeneralPurpose Input-Output), symbolized by a single block 212 (GPIO); a secondtransceiver, for example of the universal asynchronous type, 213(Universal Asynchronous Receiver Transmitter—UART); and a memory module214 (RAM), for example a volatile storage memory.

In FIG. 1, the first transceiver 210 is coupled, preferably connected,to the antenna 20 of the card 2. This transceiver in particular allowsthe card 2 to receive the radiofrequency signals emitted by the terminal1 when this card 2 is located within range of this terminal 1. The card2 thus communicates with the outside by a radiofrequency signal.

The energy harvesting module 211 is, in particular, configured to drawelectrical energy on the electromagnetic field emitted by the terminal1. This module 211 in particular serves to supply electricity to thefirst element 21. The first element 21 supplies electricity to thesecond element 22 and the biometric sensor 23 of the card 2.

The input-output terminals 212 of the first element 21 are coupled,preferably connected, to the second element 22. These terminals 212 canbe configured either to serve as an input, in other words, to receive asignal, or to serve as an output, in other words to transmit a signal.The terminals 212 allow two-way data exchanges between the first element21 and the second element 22 means of a link 24 symbolized, in FIG. 1,by a double arrow.

Still in FIG. 1, the second transceiver 213 of the first element 21 iscoupled, preferably connected, to a module 25 (MICRO MODULE) of the card2. This module 25 allows the card 2 to communicate with the terminal 1in a case where this card 2 is physically coupled or connected to thisterminal 1. This case corresponds to a situation where the card 2 isinserted into the terminal 1 in order to make a payment with contact. Insuch a situation, the exchange of data and the supply of the card 2 bothgo through conductive tracks located on the front face of this card 2.

The card 2 can also include one or several other electronic elements orcircuits. These electronic elements or circuits, the operation of whichwill not be described in detail in the description below, are symbolizedin FIG. 1 by a single functional block 26 (FCT).

It should be noted that the schematic illustration of FIG. 1 is notmeant to faithfully reproduce an actual physical arrangement of thedevices 1 and 2. In particular, the various elements that make up theterminal 1 and the card 2 are not shown to scale and can, in practice,be arranged differently from what is illustrated in FIG. 1.

FIG. 2 shows, schematically and in block diagram form, an embodiment ofthe circuits 21 and 22 of the device 2 of the system. These circuits 21and 22 communicate with one another through the wired connection 24.

According to this embodiment, the first circuit 21 includes fourinput-output terminals 212 (GPIO), for example universal: a firstterminal 212A coupled, preferably connected, to a first conductor orwire 24A configured to transmit a first channel conveying asynchronization or clock signal (CLK); a second terminal 212B coupled,preferably connected, to a second conductor or wire 24B configured totransmit third and fourth channels respectively conveying two datasignals (DATA); a third terminal 212C coupled, preferably connected, toa third conductor or wire 24C configured to transmit a fourth channelconveying a third signal (SE_BUSY); and a fourth terminal 212D coupled,preferably connected, to a fourth conductor or wire 24D configured totransmit a fifth channel conveying a fourth signal (BioMCU_BUSY).

Similarly, the second circuit 22 includes four universal input-outputterminals 222 (GPIO): a first terminal 222A coupled, preferablyconnected, to the first conductor 24A; a second terminal 222B coupled,preferably connected, to the second conductor 24B; a third terminal 222Ccoupled, preferably connected, to the third conductor 24C; and a fourthterminal 222D coupled, preferably connected, to the fourth conductor24D.

According to this embodiment, the first circuit 21 further includes: afifth terminal 215A coupled, preferably connected, to a fifth conductoror wire 27A brought to an electrical potential (VCC) making it possibleto supply the second circuit 22 from the first circuit 21; and a sixthterminal 215B coupled, preferably connected, to a sixth conductor orwire 27B brought to a reference potential, for example the ground (GND).

Similarly, the second circuit 22 further includes: a fifth terminal 225Acoupled, preferably connected, to the fifth conductor 27A; and a sixthterminal 225B coupled, preferably connected, to the sixth conductor 27B.

According to an embodiment, the fingerprint sensor 23 (FIG. 1) includestwo terminals similar to the terminals 225A and 225B of the secondcircuit 22. These two terminals of the sensor 23 are then respectivelycoupled, preferably connected, to the conductors 27A and 27B. Thefingerprint sensor 23 is then supplied with electricity by the firstcircuit 21.

In general, a master device (Master) coupled to a slave device (Slave)by a synchronous serial data bus (Serial Peripheral Interface—SPI)communicates according to a master-slave scheme, in which the masterdevice controls the communication. In practice, such as serial data bustypically includes four conductors, each conveying a signal in aunidirectional manner. In other words, each signal is transmitted eitherfrom the master toward the slave, or from the slave toward the master.

Traditionally, a synchronous serial data bus between a master device anda slave device more specifically includes: a first conductor conveying aclock signal, generated by the master device; a second conductorconveying a first data signal (Master Output, Slave Input—MOSI),generated by the master device for the slave device; a third conductorconveying a second data signal (Master Input, Slave Output—MISO),generated by the slave device for the master device; and a fourthconductor conveying a selection signal of the slave device, generated bythe master device.

Contrary to the conventional case described hereinabove, the firstcircuit 21 and the second circuit 22 of the embodiment of FIG. 2 herecommunicate with one another through a data bus SPI made up solely oftwo conductors, the conductors 24A and 24B of the link 24, according tothis embodiment. The first circuit 21 constitutes a master circuit,while the second circuit 22 constitutes a slave circuit. The dataexchanges between the first circuit 21 and the second circuit 22 takeplace at the initiative of the first circuit 21.

Here, advantage is taken of the fact that the circuits 21 and 22 are theonly two circuits that wish to communicate with one another. The usualselection signal is therefore not necessary.

The first conductor 24A here conveys the synchronization signal CLK,configured to pace the data exchanges between the master circuit 21 andthe slave circuit 22. The second conductor 24B conveys the data signalDATA, representative of the data exchanged between the master circuit 21and the slave circuit 22. More specifically, still according to thisembodiment, the second conductor 24B is configured sometimes to conveythe data signal MOSI, emitted by the master circuit 21 to the slavecircuit 22, and sometimes to convey the data circuit MISO, emitted bythe slave circuit 22 to the master circuit 21. The data signal DATA thuscorresponds either to the signal MOSI or to the signal MISO, as afunction of the direction in which the data are exchanged.

Such a communication, between the first circuit 21 and the secondcircuit 22, is qualified as half-duplex bidirectional, or “SPI IP”,communication. This SPI IP mode has the advantage of reducing the numberof terminals or pins or pads involved for the communication between thecircuits 21 and 22, in particular due to the alternating transmission ofthe MOSI and MISO signals on the same conductor 24B. The embodimentdisclosed in relation with FIG. 2 therefore makes it possible to limitthe number of hardware interfaces, terminals or conductors, used for thecommunication between these circuits 21 and 22.

According to a preferred embodiment, the third signal SE_BUSY and thefourth signal BioMCU_BUSY are binary signals, evolving between a highlevel and a low level. These signals SE_BUSY and BioMCU_BUSY, inparticular, make it possible to synchronize data exchanges between thefirst circuit 21 and the second circuit 22.

The signals SE_BUSY and BioMCU_BUSY are configured to control an exitfrom a standby mode, or low power consumption mode, of the first circuit21 and the second circuit 22. These signals SE_BUSY and BioMCU_BUSY arefurther configured to control a placement in standby mode of this firstcircuit 21 and this second circuit 22. This makes it possible to managethe power consumption of the second device 2 to which the first circuit21 and the second circuit 22 belong. It is thus, in particular, possibleto reduce the electrical power consumption of the second device 2relative to a similar device whose first and second circuits are notswitched to standby mode.

The first circuit 21 can, for example, be a microcontroller unit havingfour input-output terminals initially configured to allow a conventionalcommunication SPI on four wires. Such a circuit can advantageously bereconfigured to be made compatible with the communication methoddescribed in this disclosure. One thus retains, for an unchanged numberof wires, functionalities close to those of a conventional SPIcommunication between a master device or circuit and a slave device orcircuit, while adding the possibility of exchanging the two signalsSE_BUSY and BioMCU_BUSY between these devices or circuits.

According to a preferred embodiment, the input-output terminals 212 ofthe first circuit 21 are configured as follows: the first terminal 212Ais configured as an output, in order to transmit the signal CLK to thesecond circuit 22; the second terminal 212B is alternatively configuredas an input, to receive the signal MISO transmitted by the secondcircuit 22, or as output, to transmit the signal MOSI to this secondcircuit 22; the third terminal 212C is configured as an output, in orderto transmit the signal SE_BUSY to the second circuit 22; and the fourthterminal 212D is configured as an input, to receive the signalBioMCU_BUSY transmitted by the second circuit 22.

Still according to this preferred embodiment, the input-output terminals222 of the second circuit 22 are configured as follows: the firstterminal 222A is configured as an input, to receive the signal CLKtransmitted by the first circuit 21; the second terminal 222B isalternatively configured as an input, to receive the signal MOSItransmitted by the first circuit 21, or as output, to transmit thesignal MISO to this first circuit 21; the third terminal 222C isconfigured as an input, to receive the signal SE_BUSY transmitted by thefirst circuit 21; and the fourth terminal 222D is configured as anoutput, to transmit the signal BioMCU_BUSY to the first circuit 21.

In a variant, the first circuit 21 and the second circuit 22 eachinclude only three input-output terminals, these terminals beingcoupled, preferably connected, to three conductors: a first conductorconfigured to transmit first and second channels respectively conveyingthe synchronization signal CLK and the signal SE_BUSY, these two signalsnot being transmitted at the same time; a second conductor configured totransmit third and fourth channels respectively conveying the signalsMOSI and MISO; and a third conductor configured to transmit a fifthchannel conveying the signal BioMCU_BUSY.

According to this variant: the terminals of the first circuit 21coupled, preferably connected, to the first conductor are configured asoutputs, in order to transmit either the synchronization signal CLK, orthe signal SE_BUSY; and the terminals of the second circuit 22 coupled,preferably connected, to this first conductor are configured as inputs,in order to receive either the synchronization signal CLK, or the signalSE_BUSY.

An advantage of this variant is to make it possible to use only threeconductors. In a situation where the first and second circuits 21, 22each include four terminals, only three of these terminals are used tocarry out the method described in this disclosure. One thus frees oneterminal of each circuit and a fourth conductor to perform otherfunctions.

The role of the signals CLK, DATA, SE_BUSY and BioMCU_BUSY is disclosedin more detail below in an embodiment of a communication methoddescribed in relation with FIGS. 3 to 8.

FIG. 3 is a flowchart of phases of an embodiment of a communicationmethod between the first circuit 21 and the second circuit 22. Inparticular, FIG. 3 illustrates a progression of steps or phases of acommunication between these circuits 21 and 22 as a function of time(t).

According to this embodiment, a communication between the first circuit21, or master circuit 21, and the second circuit 22, or slave circuit22, is still engaged by the master circuit 21. In other words, it isassumed that the elements of the biometric environment of the device 2,in other words the slave circuit 22 and the fingerprint sensor 23, donot trigger communications with the master circuit 21.

The communication between the master circuit 21 (SE) and the slavecircuit 22 (BioMCU) is done according to phases for: sending commands,from the master circuit 21 to the slave circuit 22, symbolized in FIG. 3by arrows 31 (command phase); and sending responses, from the slavecircuit 22 to the master circuit 21, symbolized in FIG. 3 by arrows 32(response phase).

These command sending phases 31 and these response sending phases 32 aresuspended by periods during which the master circuit 21 and the slavecircuit 22 are respectively switched into low power modes 33 and 34.Each low power mode 33, 34 here corresponds to a standby mode, that isto say, a mode in which the electrical power consumption of the circuit21, 22 is greatly reduced relative to an electrical power consumption ofthis same circuit 21, 22 during normal operation. This reduction in theelectrical power consumption preferably consists of going from a nominalmode in which the consumption is about 10 mA to a standby mode in whichthe consumption is about 500 μA.

Before the transmission of the first command 31 by the master circuit 21and after the transmission of each response to the slave circuit 22, theslave circuit 22 is placed or switched in low power mode 34. Similarly,the master circuit 21 is placed or switched in low power mode when themaster circuit 21 is waiting for a response 32 from the slave circuit22. Each circuit 21, 22 leaves low power mode 33, 34 during the sendingof a command 31 or a response 32.

As illustrated in FIG. 3, the sending of each response 32 can beseparated from the sending of the associated command 31 by a larger orsmaller duration. This duration is in particular a function of a numberof operations executed by the slave circuit 22 in order to develop theresponse to be sent. These operations correspond to microprocessor unitinstructions or groups of microprocessor unit instructions, executed bythe slave circuit 22, for example instructions or groups of instructionsassociated with image processing operations. The sending of each command31 can also be separated from the sending of the preceding response by alarger or smaller duration. This duration is in particular a function ofa number of operations executed by the master circuit 21 in order todevelop the next command to be sent. These operations correspond tomicroprocessor unit instructions or groups of microprocessor unitinstructions, executed by the master circuit 21.

The command 31 sending phases and the response 32 sending phases areeach reflected by an exchange, between the circuits 21 and 22, of atleast two frames. Depending on whether these phases include data to becommunicated, the frames are more specifically exchanged as follows: fora command 31 sending phase without data exchange, the master circuit 21sends a command header frame, then the slave circuit 22 sends anacknowledgment frame; for a command 31 sending phase with data exchange,the master circuit 21 sends a command header frame, then the slavecircuit 22 sends an acknowledgment frame, next the master circuit sendsa command data frame and lastly the slave circuit 22 sends anotheracknowledgment frame; for a response 32 sending frame without dataexchange, the slave circuit 22 sends a response header frame, then themaster circuit sends an acknowledgment frame; and for a response 32sending phase with data exchange, the slave circuit 22 sends a responseheader frame, then the master circuit 21 sends an acknowledgment frame,next the slave circuit 22 sends a response data frame and lastly themaster circuit 21 sends another acknowledgment frame.

FIGS. 4A and 4B show timing diagrams of phases of the embodiment of thecommunication method between the circuits 21 and 22. These timingdiagrams in particular reflect an evolution, as a function of time (t),of the signals SE_BUSY, BioMCU_BUSY, CLK and DATA.

The timing diagram of FIG. 4A corresponds to a command transmission 31(FIG. 3) without data exchange while the timing diagram of FIG. 4Bcorresponds to a command transmission 31 (FIG. 3) with data exchange.

In FIG. 4A, at an initial instant t0, all of the signals SE_BUSY,BioMCU_BUSY, CLK and DATA are at a low state or level. One assumes: thatthe master circuit 21 is not in low power mode at this instant t0; andthat the slave circuit 22 is in low power mode at this instant t0.

At an instant t1, after the instant t0, the signal SE_BUSY is switchedfrom the low state to a high state or level by the master circuit 21.This transition to the high state of the signal SE_BUSY is intended tosignify to the slave circuit 22 that the master circuit 21 wishes tosend it a command. The slave circuit 22 is then taken out of low powermode and begins a wakeup sequence during which this slave circuit 22performs various operations related to its exit from standby. The signalBioMCU_BUSY is kept in the low state during all of these operations.

At an instant t2, after the instant t1, the signal BioMCU_BUSY isswitched from the low state to a high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 is readyto receive a command header frame. From the instant t2, the mastercircuit 21 and the slave circuit 22 are both kept out of low power modeuntil the end of the command sending phase.

At an instant t3, after the instant t2, the master circuit 21 begins tosend its clock signal, that is to say, it periodically switches theclock signal CLK between a low state and a high state. The firstswitching of the signal CLK from the low state to the high state marksthe beginning of the sending of the command header frame. Upon eachswitch to the high state of the signal CLK, a new bit of the commandheader frame is sent to the slave circuit 22. The command header frameis sent from the master circuit 21 to the slave circuit 22. The sendingof this command header frame therefore corresponds, as described inrelation with FIG. 2, to the sending of the signal MOSI over the secondconductor 24B of the link 24.

At an instant t4, after the instant t3, the master circuit 21 ceases toemit its clock signal CLK by returning this clock signal CLK to the lowstate. This last switching of the signal CLK from the high state to thelow state marks the end of the sending of the command header frame.

At an instant t5, after the instant t4, the signal BioMCU_BUSY isswitched from the high state to the low state by the slave circuit 22.This transition to the low state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 isoccupied executing operations allowing it to generate the acknowledgmentframe.

At an instant t6, after the instant t5, the signal BioMCU_BUSY isswitched from the low state to the high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 is readyto send the acknowledgment frame, in response to the command headerframe previously received.

At an instant t7, after the instant t6, the master circuit 21 begins toemit its clock signal. The first switching of the signal CLK from thelow state to the high state marks the beginning of the sending of theacknowledgment frame (ack). Upon each switching to the high state of thesignal CLK, a new bit of the acknowledgment frame is sent to the mastercircuit 21. The acknowledgment frame is sent from the slave circuit 22to the master circuit 21. The sending of this acknowledgment frametherefore corresponds, as described in relation with FIG. 2, to thesending of the signal MISO over the second conductor 24B of the link 24.

At an instant t8, after the instant t7, the master circuit 21 ceases toemit its clock signal CLK by returning this clock signal CLK to the lowstate. This last switching of the signal CLK from the high state to thelow state marks the end of the sending of the acknowledgment frame.

At an instant t9, after the instant t8, the signal BioMCU_BUSY isswitched from the high state to the low state by the slave circuit 22.This transition to the low state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 isoccupied executing operations allowing it to generate the response frame(not shown in FIG. 4).

At an instant t10, after the instant t9 with a duration set by themaster circuit 21, the signal SE_BUSY is switched from the high state tothe low state by the master circuit 21. The instant t10 marks the end ofthe command sending phase 31 (FIG. 3). The transition to the low stateof the signal SE_BUSY is therefore preferably accompanied by a switchingof the master circuit 21 to the low power state while waiting for aresponse sending phase initiated by the slave circuit 22. In otherwords, the master circuit 21 is placed in standby mode after having senta command to the slave circuit 22.

The timing diagram of FIG. 4B comprises common elements with the timingdiagram of FIG. 4A. These elements will not be described in detail againbelow. The timing diagram of FIG. 4B differs from the timing diagram ofFIG. 4A primarily in that the timing diagram of FIG. 4B includessuccessive moments t2′ to t9′ intercalated between the instant t9 andthe instant t10. The instant t9 is thus separated from the instant t10by a duration allowing the exchange of the command datum between thecircuits 21 and 22.

At the instant t2′, after the instant t9, the signal BioMCU_BUSY isswitched from the low state to the high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 is readyto receive a command data frame.

At an instant t3′, after the instant t2′, the master circuit 21 beginsto emit its clock signal. The first switching of the signal CLK from thelow state to the high state marks the beginning of the sending of thecommand data frame (command data). Upon each switch to the high state ofthe signal CLK, a new bit of the command data frame is sent to the slavecircuit 22. The command data frame is sent from the master circuit 21 tothe slave circuit 22. The sending of this command data frame thereforecorresponds, as described in relation with FIG. 2, to the sending of thesignal MOSI over the second conductor 24B of the link 24.

At an instant t4, after the instant t3, the master circuit 21 ceases toemit its clock signal CLK by returning this clock signal CLK to the lowstate. This last switching of the signal CLK from the high state to thelow state marks the end of the sending of the command data frame.

The evolution of the signals SE_BUSY, BioMCU_BUSY, CLK and DATA at thesuccessive moments t5′, t6′, t7′, t8′ and t9′ is next similar to whatwas previously described for the successive moments t5, t6, t7, t8 andt9, respectively. The acknowledgment frame (ack) sent between themoments t7′ and t8′ and the acknowledgment frame sent between themoments t7 and t8 can nevertheless have a different content.

According to a preferred embodiment, each command header frame includes:a first byte corresponding to an identifier of the command to beexecuted by the slave circuit 22; a second byte corresponding to anenergy (power budget) supplied by the electromagnetic field EMF (FIG.1), in other words an energy that can be allocated to the biometricframework for the execution of its operations, or to an available power;a third byte corresponding to a remaining activity duration value (timebudget) of the device 2 (FIG. 1), in other words a duration that can beallocated to the biometric framework for the execution of itsoperations; a fourth duration making it possible to indicate, to thesecond circuit 22, whether the command sent by the first circuit 21constitutes a new command or an instruction to continue execution of aprevious command; two bytes corresponding to a data length to be sent;and two other bytes corresponding to a result of a Cyclic RedundancyCheck (CRC).

The value of the second byte is preferably representative of anintensity of an electric supply current of the device 2 from theelectromagnetic field EMF sent by the terminal 1 (FIG. 1). A macrocellof the first circuit 21 then adapts the operating frequency of thisfirst circuit 21 as a function of this intensity estimate. The firstcircuit 21 can send the available energy value to another circuit nothaving such a macrocell, for example the second circuit 22, in order toallow this second circuit 22 to adapt its operating frequency accordingto the energy that can be delivered to it. The operating frequency ofthe second circuit 22 can thus be adapted as a function of the energy,here the electrical intensity, able to be allocated to this secondcircuit 22.

According to this embodiment, the intensity from the electromagneticfield EMF captured by the antenna 20 (FIG. 1) of the device 2 isestimated by a sensor of the first circuit 21. As an example, theintensity is between about 2.5 mA and about 17.5 mA per 0.5 mA pitch fora module of the magnetic component of the EMF field varying between 0.5A/m and 3 A/m, per pitch of 0.1 A/m. This range of intensities thenincludes 32 possible values, which allows it to be encoded on 5 bits ofthe second byte to send it to the second circuit 22.

Likewise, the time budget value is estimated by the first circuit 21 andsent to the second circuit 22.

In a variant, the fourth byte corresponds to a voltage budget supplyingthe device 2 (FIG. 1), in other words, a voltage that can be allocatedto the biometric framework for the execution of its operations. Thevoltage value allows the second circuit 22 to adapt an internalconfiguration. The second circuit 22 can for example consume a greateror lesser electrical current depending on the voltage value sent to itby the first circuit 21.

FIGS. 5A and 5B show timing diagrams of other phases of the embodimentof the communication method between the circuits 21 and 22. These timingdiagrams in particular reflect an evolution, as a function of time (t),of the signals SE_BUSY, BioMCU_BUSY, CLK and DATA.

The timing diagram of FIG. 5A corresponds to a response transmission 32(FIG. 3) without data exchange while the timing diagram of FIG. 5Bcorresponds to a response transmission 32 (FIG. 3) with data exchange.

The timing diagrams of FIGS. 5A-5B comprise common elements with thetiming diagrams of FIGS. 4A-4B. These elements will not be described indetail again below. The timing diagrams of FIGS. 5A-5B differ from thetiming diagrams of FIGS. 4A-4B primarily in that, in the timing diagramsof FIGS. 5A-5B, it is the master circuit 21 that is removed, by theslave circuit 22, from low power mode. The signals are furtherexchanged, in FIGS. 5A-5B, in the opposite direction relative to whatwas described in relation with FIGS. 4A-4B.

In FIG. 5A, at the initial instant t0, all of the signals SE_BUSY,BioMCU_BUSY, CLK and DATA are in the low state (at the low level). It isassume, contrary to what was described in relation with FIGS. 4A-4B:that the master circuit 21 is in low power mode at this instant t0; andthat the slave circuit is not in low power mode at this instant t0. InFIGS. 5A-5B, the signal SE_BUSY is kept in the low state during theentire response sending phase.

At the instant t1, the signal BioMCU_BUSY is switched from the low stateto a high state by the slave circuit 22. The transition to the highstate of the signal BioMCU_BUSY is intended to signify to the mastercircuit 21 that the slave circuit 22 wishes to send it a response. Themaster circuit 21 is then taken out of low power mode and begins awakeup sequence during which this master circuit 21 performs variousoperations related to its exit from standby. The master circuit 21 andthe slave circuit 22 are both kept out of low power mode until the endof the response sending phase.

Between the moments t3 and t4, the master circuit 21 emits its clocksignal CLK and bits of the response header frame are sent to the mastercircuit 21 upon each period of this signal CLK. The response headerframe is sent from the slave circuit 22 to the master circuit 21. Thesending of this response header frame therefore corresponds, asdescribed in relation with FIG. 2, to the sending of the signal MISOover the second conductor 24B of the link 24.

Between the moments t7 and t8, the master circuit 21 emits its clocksignal CLK and bits of the acknowledgement (ack) frame are sent to theslave circuit 22 upon each period of this signal CLK. The acknowledgmentframe is sent from the master circuit 21 to the slave circuit 22. Thesending of this acknowledgment frame therefore corresponds, as describedin relation with FIG. 2, to the sending of the signal MOSI over thesecond conductor 24B of the link 24.

At the instant t9, the signal BioMCU_BUSY is switched from the highstate to the low state by the slave circuit 22. According to thisembodiment, the signal SE_BUSY is kept in the low state between themoments t0 and t9. The timing diagram of FIG. 5A thus does not includean instant t10, unlike the timing diagrams previously disclosed inrelation with FIGS. 4A-4B.

The timing diagram of FIG. 5B comprises common elements with the timingdiagram of FIG. 5A. These elements will not be described in detail againbelow. The timing diagram of FIG. 5B differs from the timing diagram ofFIG. 5A primarily in that the timing diagram of FIG. 5B includessuccessive moments t2′ to t9′ after the instant t9. The instant t9 isthus followed by a duration allowing the exchange of the response datumbetween the circuits 21 and 22.

At the instant t2′, the signal BioMCU_BUSY is switched from the lowstate to the high state by the slave circuit 22. This transition to thehigh state of the signal BioMCU_BUSY is intended to signify to themaster circuit 21 that the slave circuit 22 is ready to send a responsedata frame.

At an instant t3′, the master circuit 21 begins to emit its clocksignal. The first switching of the signal CLK from the low state to thehigh state marks the beginning of the sending of the response data frame(response data). Upon each switching to the high state of the signalCLK, a new bit of the response data frame is sent to the master circuit21. The response data frame is sent from the slave circuit 22 to themaster circuit 21. The sending of this response data frame thereforecorresponds, as described in relation with FIG. 2, to the sending of thesignal MISO over the second conductor 24B of the link 24.

At an instant t4′, the master circuit 21 ceases to emit its clock signalCLK by returning this clock signal CLK to the low state. This lastswitching of the signal CLK from the high state to the low state marksthe end of the sending of the response data frame.

The evolution of the signals SE_BUSY, BioMCU_BUSY, CLK and DATA at thesuccessive moments t5′, t6′, t7′, t8′ and t9′ is next similar to whatwas previously described for the successive moments t5, t6, t7, t8 andt9, respectively. The acknowledgment frame (ack) sent between themoments t7′ and t8′ and the acknowledgment frame sent between themoments t7 and t8 can nevertheless have a different content. Theacknowledgment frame sent between the moments t7′ and t8′ and theacknowledgment frame sent between the moments t7 and t8 are here, unlikewhat was described in relation with FIGS. 4A-4B, emitted by the mastercircuit 21 to the slave circuit 22.

At the instant t9′, the signal BioMCU_BUSY is switched from the highstate to the low state by the slave circuit 22. According to thisembodiment, the signal SE_BUSY is kept in the low state between themoments t0 and t9′. The timing diagram of FIG. 5B thus does not includean instant t10, unlike the timing diagrams disclosed in relation withFIGS. 4A-4B.

According to a preferred embodiment, each response header frameincludes: two first bytes corresponding to a status of the commandexecuted by the slave circuit 22; a second byte making it possible toindicate, to the master circuit 21, whether the slave circuit 22 iswaiting to receive a new command or a command with the same identifierfor which it is meant to continue the execution; a third bytecorresponding to a maximum sending frequency value, on the link 24(FIGS. 1 and 2), compatible with the energy that can be allocated by themaster circuit 21 to the biometric framework; two bytes corresponding toa data length to be sent; and two other bytes corresponding to a resultof a Cyclic Redundancy Check (CRC).

The value of the third byte of the response frame in particular makes itpossible for the master circuit 21 to adapt the sending frequency on thelink as a function of variations of the energy coming from theelectromagnetic field. An increase in the energy can, in particular,lead to an increase in the sending frequency. Conversely, a decrease inthe energy can lead to a decrease in the sending frequency.

According to this embodiment, a response sending by the slave circuit 22is preceded by a command sending by the master circuit 21. Differentcases of alternating sequences of commands and responses are thuspossible, depending on whether these commands and/or these responsesinclude data, the implementation of these different cases being withinthe capabilities of one skilled in the art from the above information.

According to a preferred embodiment, error management operations areprovided in case of malfunction affecting the slave circuit 22. Duringnormal operation, each placement in the high state of the signal SE_BUSYis meant to be accompanied, several moments later, by a placement in thehigh state of the signal BioMCU_BUSY. A time delay is launched at thetime of the switching to the high state of the signal SE_BUSY. In thecase where the master circuit 21 observes that the signal BioMCU_BUSYhas not been switched to the high state before expiration of the timedelay, it is considered that the slave circuit 22 is not responding.

Still according to this preferred embodiment, one or several other timedelays are launched after the sending of a command header, a responseheader, a command and/or a response. In the case where this or theseother time delay(s) expire before the associated acknowledgment frame issent, it is considered that the slave circuit 22 is not responding.

Furthermore, if the acknowledgment frame does not contain the valueexpected by the recipient circuit of this frame, the preceding frame maybe resent. In the case where several successive acknowledgment frames donot contain the expected value, for example after three successiveacknowledgment frames not corresponding to the frame expected by therecipient circuit, it may also be considered that the slave circuit 22is not responding.

FIG. 6 is a timing diagram of still another phase of the embodiment ofthe communication method between the circuits 21 and 22. This timingdiagram in particular reflects an evolution, as a function of time (t),of the signals SE_BUSY, BioMCU_BUSY, CLK and DATA.

The timing diagram of FIG. 6 corresponds to a response sending 32 (FIG.3) with data exchange, in a situation where the length or size of theresponse datum, that is to say, the number of bytes of this datum,exceeds the limit length of a frame. This situation for examplecorresponds to a case where the slave circuit 22 sends the mastercircuit 21 a datum representative of analysis results of a fingerprintwhose length exceeds the limit length of a frame.

It is assumed, for the communication method implemented on the link 24,that the limit length of a frame is equal to 240 bytes. When the lengthof the response datum to be sent is greater than 240 bytes, this datumis divided into as many words as necessary, each word not exceeding 240bytes. The sending of the response datum then amounts to performing,during a same response phase 32 (FIG. 3), successive transmission offrames each corresponding to a word of the response datum.

FIG. 6 illustrates, as an example, a situation in which the slavecircuit 22 sends, to the master circuit 21, a response datum including500 bytes. This datum including 500 bytes is, still in this example,divided into: a first word (response data [0-239]) made up of the first240 bytes of the response datum; a second word (response data [240-479])made up of the following 240 bytes of the response datum; and a thirdword (response data [480-499]) made up of the last 20 bytes of theresponse datum.

The timing diagram of FIG. 6 comprises common elements with the timingdiagram of FIG. 5B. These elements will not be described in detail againbelow. The timing diagram of FIG. 6 differs from the timing diagram ofFIG. 5B primarily in that the operations separating the moments t2′ tot6′ described in relation with FIG. 5B are repeated several times inFIG. 6. In particular, successive moments t2′a, t3′a, t4′a, t5′a, t2′b,t3′b, t4′b, t5′b, t2′c, t3′c, t4′c and t5′c are intercalated between themoments t9 and t6′.

At the instant t2′a, which is analogous to the instant t2′ of FIG. 5B,the signal BioMCU_BUSY is switched from the low state to the high stateby the slave circuit 22. This transition to the high state of the signalBioMCU_BUSY is intended to signify to the master circuit 21 that theslave circuit 22 is ready to send a first frame containing the firstword of the response datum.

At the instant t3′a, which is analogous to the instant t3′, the mastercircuit 21 begins to emit its clock signal. The first switching of thesignal CLK from the low state to the high state marks the beginning ofthe sending of the first frame. Upon each switching to the high state ofthe signal CLK, a new bit of the first frame, therefore of the firstword, is sent to the master circuit 21. The first frame is sent from theslave circuit 22 to the master circuit 21. The sending of this firstframe therefore corresponds, as described in relation with FIG. 2, tothe sending of the signal MISO over the second conductor 24B of the link24.

At an instant t4′a, which is analogous to the instant t4′, the mastercircuit 21 ceases to emit its clock signal CLK by returning this clocksignal CLK to the low state. This last switching of the signal CLK fromthe high state to the low state marks the end of the sending of thefirst frame.

At the instant t5′a, which is analogous to the instant t5′, the signalBioMCU_BUSY is switched to the low state. The slave circuit 22 thusindicates to the master circuit 21 that it is not ready to send or toreceive.

The signals SE_BUSY, BioMCU_BUSY, CLK and DATA next evolve at thesuccessive moments t2′b, t3′b, t4′b and t5′b after the instant t5′a,similarly to what was described previously for the successive momentst2′a, t3′a, t4′a and t5′a, respectively, with the sole difference thatthe moments t3′b and t4′b frame the sending of a second frame containingthe second word of the response datum. Similarly, the signals SE_BUSY,BioMCU_BUSY, CLK and DATA next evolve at the successive moments t2′c,t3′c, t4′c and t5′c after the instant t5′b, similarly to what wasdescribed previously for the successive moments t2′a, t3′a, t4′a andt5′a, respectively, with the sole difference that the moments t3′c andt4′c frame the sending of a third frame containing the third word of theresponse datum.

During a contactless communication, an effort is made so that the firstcircuit 21, the second circuit 22 and the biometric sensor 23 consume aslittle energy as possible. Preferably, the biometric framework, that isto say, the second circuit 22 and the biometric sensor 23, are thus onlytaken out of low power mode in two cases: during an initial start-upphase, during which the card (FIG. 1) is brought closer to the terminal1 (FIG. 1) so that this card is powered by this terminal 1; and betweenthe beginning of a command sending phase 31 (FIG. 3) and the end of theassociated response sending phase 32 (FIG. 3). Outside of these twocases, the biometric framework is placed in standby mode after each endof response sending phase 32.

In a variant, the biometric framework is only supplied when it isstressed by the first circuit 21. The biometric framework is thenstarted upon stress from the first circuit 21 and the sending of a firstcommand is initiated by the first circuit 21 when the signal BioMCU_BUSYis switched to the low state.

According to an embodiment, a suspension sometimes occurs during anactivity period of the biometric framework, between the sending of acommand and the sending of the associated response. In practice, thissuspension can appear in case of a wait time extension (WTX) request.Such a wait time extension request in particular occurs when the card 2needs the terminal 1 to grant it additional time before stopping theemission of the field, therefore cutting the supply of this card 2.

For banking applications of the contactless payment type, the wait timeextension request is typically sent after about 38 ms, at most: afterreception of an application protocol data unit (APDU) command; or afterreception of the last wait time extension request.

According to a preferred embodiment, a time delay or timer is activatedby the first circuit 21 after each APDU reception or wait time extensionrequest reception. An expiration of this time delay then makes itpossible to indicate, to the first circuit 21, an opportune instant tomake the next time delay extension request. This time delay is, in thisexample, initially set at a value of less than 38 ms.

If this time delay expires at an instant where the second circuit 22 isnot in low power mode, in other words if this time delay expires whilethe second circuit 22 is active, the first circuit 21 then sends thissecond circuit 22 a suspension command. This suspension command seeks tosuspend operations performed by the second circuit 22 and to temporarilyswitch this second circuit 22 to low power mode.

FIG. 7 is a timing diagram of still another phase of the embodiment ofthe communication method between the circuits 21 and 22, in case ofsending of a suspension command. This timing diagram in particularreflects an evolution, as a function of time (t), of the signalsSE_BUSY, BioMCU_BUSY, CLK and DATA.

The timing diagram of FIG. 7 corresponds to a situation in which thetime delay expires while the slave circuit 22 is active. The mastercircuit 21 will therefore send a suspension command to the slave circuit22 in order to place this second circuit in low power mode.

It is assumed, in FIG. 7, that the signals SE_BUSY, BioMCU_BUSY, CLK andDATA are initially all in the low state at an instant t20. It is furtherassumed that this instant t20 is intercalated between a command sendingphase and a response sending phase. The signal BioMCU_BUSY is thus meantto go to the high state after the instant t20 to initiate a responsesending phase. In FIG. 7, contrary to what one might expect (since oneis meant to begin a response sending phase, normally the rising of thesignal BioMCU_BUSY is expected), it is the signal SE_BUSY that is placedin the high state for the instant t20.

At an instant t21, after the instant t20, the signal SE_BUSY is thusswitched from the low state to the high state by the master circuit 21.This transition to the high state of the signal SE_BUSY is intended tosignify to the slave circuit 22 that the master circuit 21 wishes tosuspend it.

From the instant t21, the slave circuit 22 detects and executes thesuspension command. This slave circuit 22 is switched to low power mode.After a duration, denoted Max Suspend Time, operations (WTX management)to manage the time extension request are then performed by the mastercircuit 21. The Max Suspend Time duration is great enough to guaranteethat the slave circuit 22 has indeed switched to low power mode beforebeginning max suspend time management operations. The slave circuit 22is thus placed in standby mode during a communication of the mastercircuit 21 with the outside of the card 2 (FIG. 1).

At an instant t23, after the instant t21, the signal SE_BUSY is thusswitched from the high state to the low state by the master circuit 21.The instant t23 marks the end of the management of the max suspend timeby this master circuit 21. The switching of the signal SE_BUSY to thelow state causes the slave circuit 22 to exit the low power mode. Thisamounts to sending the slave circuit 22 a command to resume theoperations executed by this slave circuit 22 before the transmission ofthe suspension command.

The slave circuit 22 is then taken out of low power mode and begins awakeup sequence during which this slave circuit 22 performs variousoperations related to its exit from standby. The signal BioMCU_BUSY iskept in the low state during all of these operations.

At an instant t25, after the instant t23, the signal SE_BUSY is switchedfrom the low state to the high state by the master circuit 21. Thismeans that the master circuit 21 wishes to send a resume frame to theslave circuit 22.

At an instant t26, after the instant t25, the signal BioMCU_BUSY isswitched from the low state to the high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY, which herefollows the transition to the high state of the signal SE_BUSY, isintended to signify to the master circuit 21 that the slave circuit 22is ready to receive the resume frame.

At an instant t27, after the instant t26, the master circuit 21 emitsits clock signal CLK. The first switching of the signal CLK from the lowstate to the high state marks the beginning of the sending of the resumeframe. Upon each switch to the high state of the signal CLK, a new bitof the resume frame is sent to the slave circuit 22. The resume frame issent from the master circuit 21 to the slave circuit 22. The sending ofthis resume frame therefore corresponds, as described in relation withFIG. 2, to the sending of the signal MOSI over the second conductor 24Bof the link 24.

According to a preferred embodiment, the resume frame includes bytessimilar to those of a command header frame as described in relation withFIGS. 4A-4B. In particular, the resume frame includes the third bytecorresponding to the time budget allocated to the biometric frameworkfor the execution of its operations. This time budget more specificallycorresponds, still according to this preferred embodiment, to aremaining duration of the time delay suitable for providing thefollowing wait time extension. This thus advantageously allows themaster circuit 21 to communicate, to the slave circuit 22, the durationthat this slave circuit 22 has to perform its operations before the nextwait time extension.

At an instant t28, after the instant t27, the master circuit 21 stopemitting its clock signal CLK. This instant t28 thus marks the end ofthe sending of the resume frame.

At an instant t29, after the instant t28, the signal BioMCU_BUSY isswitched from the high state to the low state by the slave circuit 22.This transition to the low state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 isoccupied executing operations allowing it to generate the acknowledgmentframe.

At an instant t30, after the instant t29, the signal BioMCU_BUSY isswitched from the low state to the high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 is readyto send the acknowledgment frame, in response to the resume framepreviously received.

At an instant t31, after the instant t30, the master circuit 21 beginsto emit its clock signal and the acknowledgment frame is sent by theslave circuit 22 to the master circuit 21. The sending of thisacknowledgment frame therefore corresponds, as described in relationwith FIG. 2, to the sending of the signal MISO over the second conductor24B of the link 24.

At an instant t32, after the instant t31, the master circuit 21 stopsemitting its clock signal CLK. This instant t32 thus marks the end ofthe sending of the acknowledgment frame.

At an instant t33, after the instant t32, the signal BioMCU_BUSY isswitched from the high state to the low state by the slave circuit 22.This transition to the low state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 isoccupied continuing to execute operations allowing it to generate theresponse frame.

At an instant t34, after the instant t33, the signal SE_BUSY is thusswitched from the high state to the low state by the master circuit 21.The instant t34 marks the end of the sending of the resume frame and ofthe associated acknowledgment frame. The transition to the low state ofthe signal SE_BUSY is therefore preferably accompanied by a switching ofthe master circuit 21 to the low power state while waiting for theresponse sending phase initiated by the slave circuit 22.

At an instant t35, after the instant t34, the signal BioMCU_BUSY isswitched from the low state to the high state by the slave circuit 22.This transition to the high state of the signal BioMCU_BUSY is intendedto signify to the master circuit 21 that the slave circuit 22 wishes tosend it a response. The master circuit 21 is then taken out of low powermode and begins a wakeup sequence during which this master circuit 21performs various operations related to its exit from standby. The signalSE_BUSY is kept in the low state during all of these operations.

It is then assumed that no suspension command is sent to the slavecircuit 22 by the master circuit 21.

At an instant t37, after the instant t35, the master circuit 21 emitsits clock signal CLK and bits of the response header frame are sent tothe slave circuit 22 upon each period of this signal CLK. The responseheader frame is sent from the slave circuit 22 to the master circuit 21.The sending of this response header frame therefore corresponds, asdescribed in relation with FIG. 2, to the sending of the signal MISOover the second conductor 24B of the link 24.

According to this embodiment, a competition situation (race case),between the suspension command and the response frame sending request,may sometimes occur. Such a situation may in particular arise when themaster circuit 21 commands the suspension of the slave circuit 22approximately at the instant where the slave circuit 22 prepares to senda response. This for example corresponds to a quasi-simultaneous rise ofthe signals SE_BUSY and BioMCU_BUSY at the instant t21.

In this case, priority is given to the suspension command sent by themaster circuit 21. The signal BioMCU_BUSY is then switched to the lowstate before expiration of the Max Suspend Time duration. The suspensioncommand is next taken into account by the slave circuit 22, which entersstandby mode to allow the management of the wait time extension by themaster circuit 21.

Still according to this embodiment, the switch to the high state of thesignal SE_BUSY therefore corresponds to: the sending of a command, whenthe slave circuit 22 is in standby mode; or the sending of a suspensioncommand, when the master circuit 21 is waiting for a response from theslave circuit 22.

FIGS. 8A and 8B show flowcharts of other steps of the embodiment of thecommunication method. In particular, FIGS. 8A-8B illustrate aprogression of steps or phases of a communication between the circuits21 and 22 as a function of time (t).

According to this embodiment, the second circuit 22 performs two typesof operations or tasks: so-called interruptible tasks, in other words,operations whose execution can be suspended at any time, then resumedwithout impact on the operation; and so-called uninterruptible tasks, inother words, operations whose execution cannot be suspended until it hasbeen completed.

An example of an interruptible task is an analysis, by the secondcircuit 22, of an image obtained by the fingerprint sensor 23 in orderto extract minutiae therefrom, that is to say, to produce a reducedfingerprint. An example of an uninterruptible task is a communicationbetween the second circuit 22 and the fingerprint sensor 23.

FIG. 8A shows, schematically, a communication diagram between the firstcircuit 21 and the second circuit 22 in a case where this second circuit22 executes an interruptible operation 82. The first circuit 21 sends,to the second circuit 22, a command (arrow 81, command) to execute thisinterruptible operation 82. The second circuit 22 then begins theexecution (block 82 a, Execution) of the interruptible operation 82commanded by the first circuit 21.

After a duration corresponding to the expiration (WTX timer expiration)of the time delay making it possible to anticipate the next wait timeextension, a suspension command (arrow 83 a, suspend) is sent to thesecond device 22, as described in relation with FIG. 7. This results insuspending the execution 82 a, by the second circuit 22, of theinterruptible operation 82 and allowing the first circuit 21 to manage(block 84 a, WTX management) the wait time extension. A resume command(arrow 85 a, resume) is then sent to the second circuit 22. This secondcircuit 22 then resumes the execution (block 82 b, Execution) of theinterruptible operation 82.

After a duration corresponding to the expiration (WTX time expiration)of the time delay making it possible to anticipate the next wait timeextension, a new suspension command (arrow 83 b, suspend) is sent to thesecond device 22. This results in suspending the execution 82 b, by thesecond circuit 22, of the interruptible operation 82 and allowing thefirst circuit 21 to manage (block 84 b, WTX management) the wait timeextension. A new resume command (arrow 85 b, resume) is then sent to thesecond circuit 22. This second circuit 22 then resumes the execution(block 82 c, Execution) of the interruptible operation 82.

Once the execution 82 c of the interruptible operation 82 is complete, aresponse (arrow 86, response) is sent by the second circuit 22. Thisresponse for example contains output data of the execution 82 a, 82 b,82 c of the interruptible operation 82.

It is assumed, in FIG. 8A, that only two suspensions, each arising fromthe need to manage a wait time extension, take place during theexecution of the interruptible operation. It is understood, however,that in practice, the interruptible operation can be suspended by anynumber of suspensions, the implementation of such a variant being withinthe capabilities of one skilled in the art from the information suppliedin this disclosure.

FIG. 8B shows, schematically, a communication diagram between the firstcircuit 21 and the second circuit 22 in a case where this second circuit22 executes an operation 87, for example an interruptible operation ableto be divided or split into several uninterruptible sub-operations orsubtasks. It is assumed, according to this embodiment, that eachsub-operation can be executed during a duration shorter than theduration separating two successive wait time extensions.

The first circuit 21 sends, to the second circuit 22, a command (arrow81, command) to execute the operation 87. The second circuit 22 thenexecutes, in the example of view B, a first uninterruptiblesub-operation (block 87 b, sub-op 1), then a second uninterruptiblesub-operation (block 87 b, sub-op 2) of the operation 87 commanded bythe first circuit 21.

After a duration preceding the foreseen expiration (Foreseen WTX timerexpiration) of the time delay making it possible to foresee the nextwait time extension, a response (arrow 86 a, response (not terminated))is sent to the first device 21. This results in allowing the firstcircuit 21 to manage (block 84 a, WTX management) the wait timeextension. A resume command (arrow 88 a, command (continue)) is thensent to the second circuit 22. This second circuit 22 then executes,still in the example of FIG. 8B, a third uninterruptible sub-operation(block 87 c, sub-op n), then a fourth uninterruptible sub-operation(block 87 d, sub-op n+1) of the operation 87 commanded by the firstcircuit 21.

After a duration preceding the foreseen expiration (Foreseen WTX timerexpiration) of the time delay making it possible to foresee thefollowing wait time extension, a new response (arrow 86 b, response (notterminated)) is sent to the first device 21. This results in allowingthe first circuit 21 to manage (block 84 b, WTX management) the secondwait time extension. A new resume command (arrow 88 b, command(continue)) is then sent to the second circuit 22. This second circuit22 then executes, again in the example of view B, a fifth and finaluninterruptible sub-operation (block 87 e, sub-op m) completing theoperation 87 commanded by the first circuit 21.

It is assumed, in FIG. 8B, that only two suspensions, each arising fromthe need to manage a wait time extension, take place during theexecution of the operation. It is understood, however, that in practice,the operation can be suspended by any number of suspensions, theimplementation of such a variant being within the capabilities of oneskilled in the art from the information supplied in this disclosure.

According to a preferred embodiment, the command 81′ and the resumecommands 88 a and 88 b contain the energy budget and the time budgetallocated to the second circuit 22 until the next wait time extensionmanagement. This advantageously allows the second circuit 22 tocalculate a number of uninterruptible operations that can be executedbefore the next suspension as a function, in particular, of theavailable energy.

It is thus possible to develop a strategy for executing operations bythe second circuit 22. In a case, in particular, of an operationincluding uninterruptible sub-operations, this second circuit 22 is ableto decide how many uninterruptible sub-operations can be performedbefore the next suspension. This makes it possible to limit a risk ofsuspension during an execution of an uninterruptible sub-operation. Onethus also optimizes the execution of uninterruptible sub-operations of agiven operation.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these embodiments canbe combined and other variants will readily occur to those skilled inthe art. What has been described in relation with the embodiments andmodes of implementation in which the synchronization signal CLK is atthe low level by default, the acquisition of data being done on therising edges of the signal CLK, can be transposed to a reverse level andreverse edges (high level and falling edges).

Furthermore, what has been described in particular in relation withembodiments and modes of implementation in which the sensor 23 is afingerprint sensor more generally applies to other types of biometricsensors 23, for example facial recognition sensors.

Finally, the practical implementation of the embodiments and variantsdescribed herein is within the capabilities of those skilled in the artbased on the functional description provided hereinabove. In particular,what is more specifically described in relation with an exemplaryapplication to a communication between a microcontroller unit executingsecure operations and a biometric microcontroller unit more generallyapplies to any communication between a master circuit or device and aslave circuit or device.

The invention claimed is:
 1. A method for communication between a firstelement and at least one second element of a same device connected by acommunications link, comprising: sending by the first element to thesecond element over said communications link a first piece ofinformation representative of an energy-related power budget that issupplied to the device by an electromagnetic field, wherein the firstpiece of information is an intensity of an electrical supply current ofthe device from the electromagnetic field; and adapting by the secondelement of an operating frequency as a function of the intensity of theelectrical supply current provided by said first piece of information.2. The method according to claim 1, further comprising evaluating theintensity of the electrical supply current by the first element.
 3. Themethod according to claim 1, further comprising: sending by the firstelement to the second element a second piece of informationrepresentative of a remaining time budget of the device; and performingby the second element a number of operations as a function of the secondpiece of information.
 4. The method according to claim 3, furthercomprising evaluating the second piece of information by the firstelement.
 5. The method according to claim 1, further comprising: sendingby the first element to the second element a third piece of informationrepresentative of a voltage budget of the device; and adapting by thesecond element an internal configuration as a function of the thirdpiece of information.
 6. The method according to claim 5, furthercomprising evaluating the third piece of information by the firstelement.
 7. The method according to claim 1, wherein the first elementsupplies power to the second element.
 8. The method according to claim1, wherein the first element is a secure electronic circuit.
 9. Themethod according to claim 1, wherein the second element is amicrocontroller.
 10. The method according to claim 1, wherein the secondelement is coupled to a fingerprint sensor.
 11. The method according toclaim 10, wherein the fingerprint sensor is part of the device.
 12. Themethod according to claim 10, wherein the first element supplies powerto the fingerprint sensor.
 13. The method according to claim 1, whereinthe device externally communicates without contact using aradiofrequency signal, or communicates externally with contact using awired signal.
 14. A device configured to carry out the method accordingto claim
 1. 15. A payment card configured to carry out the methodaccording to claim 1.